Behaviour that seemingly contributes to the public good can evolve as a by-product of self-serving actions.
Andrea and Redouan Bshary at the University of Neuchâtel in Switzerland studied a type of blenny fish (Plagiotremus rhinorhynchus) that stealthily bites scalefin anthias (Pseudanthias squamipinnis; pictured) from behind.
Some victims chase the biting blenny after an attack. The authors used Plexiglass plates to mimic chasing or fleeing anthias in the lab, and found that chasing acts as a self-serving punishment, prompting blennies to pursue other individuals in future attacks. In the field, chased blennies were seen biting other prey species, suggesting that chasing also serves a public good.
Moreover, the researchers found that blennies can distinguish between chasers and those that flee or 'free-ride'. They say that free-riders might make themselves easy targets for the blennies, thereby favouring the chasing behaviour.